Re: [PATCH] Revert "net: phy: turn carrier off on phy attach"

[Clemens Gruber <clemens.gruber@pqgruber.com>]

On Fri, Feb 12, 2016 at 10:56:04AM -0800, Florian Fainelli wrote:
> On 12/02/16 10:01, Clemens Gruber wrote:
> > Commit 113c74d83eef ("net: phy: turn carrier off on phy attach") breaks
> > the eth0 link coming up on all my i.MX6Q boards with a Marvell 88E1510.
> > If I then do a ifconfig eth0 down/up cycle I first get a MDIO read
> > timeout but then the link becomes ready and everything is back to
> > normal.
> > Without this step however, the link stays down forever, an unusually
> > high amount of phy interrupts occur (about 10000/second) and kworker/0:2
> > is constantly using over 60% of the CPU.
> > 
> > Reverting it fixes the problems with the link not coming up at boot as
> > well as the high amount of phy interrupts and kworker load in that
> > state.
> 
> You are seeing this with the FEC driver right? We probably want to
> carefully audit the driver and understand what could be going wrong, the
> initial change is correct, so there must be something else going on here.

I think I found the underlying problem!
It was not the fec driver but the marvell phy driver, more specifically
the marvell_of_reg_init call being made too late, which lead to the
observed problem at half the boot ups where the link never came up.

With the marvell,reg-init device tree parameter, a flag needs to be set
to tell the Marvell 88E1510 that it should enable the interrupt output.
(At a specific pin, in my case LED[2])
If this is not set (or set too late), the phydev->state is set to UP in
phy_start (called from fec_enet_open) but then, the auto-negotiation
never starts.
In comparison, now, after I called marvell_of_reg_init not in
m88e1510_config_aneg but in marvell_probe, everything works again :)
About a second after the fec_enet_open/phy_start calls, the
auto-negotiation starts (m88e1510_config_aneg) and the phy state changes
from UP to AN, to CHANGELINK and finally to RUNNING.

I will send a patch shortly, calling marvell_of_reg_init from a new
m88e1510_probe function instead of the m88e1510_config_aneg function.

Thanks.
Clemens